1. Field of the Invention
The present invention relates to audio reproducing apparatuses and methods thereof for reducing noise to the outside while providing sound with sufficient volume.
2. Description of the Related Art
Audio-video reproducing systems referred to as “home theater systems” are becoming popular. In the audio-video reproducing systems, for example, video reproduction from a digital versatile disc (DVD) is performed by displaying a reproduced video image on a relatively large display, and sound reproduction employs a multi-channel system, recently a 5.1-channel system, thereby providing dynamic audio and video reproduction.
In the 5.1-channel sound reproducing system, six speakers of four types, namely, front, center, rear, and subwoofer, are placed at appropriate positions, and the speakers are played with relatively large volume.
That is, a front-left channel speaker is placed at the left, a front-right channel speaker is placed at the right, and a center channel speaker is placed at the center in front of a listener. A rear-left channel speaker is placed at the left and a rear-right channel speaker is placed at the right behind the listener. A subwoofer speaker for the low frequency effects (LFE) channel is placed at an appropriate position. The LFE channel carries low frequencies of about 100 to 120 Hz to provide deep bass and dynamic impact.
These six speakers are mounted on associated speaker boxes (enclosures) and placed at appropriate positions. In general, the six front and rear speakers are often placed within a distance of, for example, about 2 meters from the listener.
In such a known audio reproducing system, left (L) and right (R) speakers that have been used to be mounted on speaker boxes of about 15 liters, for example, are now mounted on small boxes of about 1 liter and are also referred to as “satellite speakers”. These speakers lack low-frequency sounds. To compensate for the lack of low-frequency sounds, a low-frequency-dedicated speaker referred to as a “subwoofer” is added. When speakers other than the subwoofer are housed in small boxes, the crossover frequency of an audio signal supplied to the subwoofer is 150 Hz, which is a quite low frequency, though this is somewhat higher than the aforementioned 100 Hz.
When a 5.1-channel audio signal is reproduced from a DVD in such a speaker system with the above-described placement, sufficient low sounds are naturally played. Since a dedicated LFE-channel is provided for reproduction, the speaker system provides “room-filling” bass from a source such as a movie, which was not achieved by known speaker systems, thereby providing dynamic impact.
In the above-described multi-channel audio reproducing system, it is necessary to turn the volume of the aforementioned six speakers relatively loud in order to enable the listener to appreciate surround localization and dynamic impact of deep bass.
In a house with less strongly built walls and floors, such sound reproduction at high volume produces unpleasant noise. In particular, low bass around 50 Hz or 40 Hz provided by the subwoofer is powerful and is conveyed through quite a wide range. It is thus difficult for the listener to appreciate a source such as a movie from a DVD with sufficient performance. This problem is particularly serious at midnight. A volume that is not noticeable during the day time because of external noises becomes annoying at night. The situation is that the function of the multi-channel audio reproducing system is hardly ever used to achieve sufficient sound volume during hours in which the user has time to see DVDs.
An exemplary solution to the problem is described in Japanese Unexamined Patent Application Publication No. 5-95591. This proposes an audio reproducing system in which middle and high frequency sounds are reproduced by small speakers (speaker units are housed in speaker boxes) and low frequencies are reproduced by a low-frequency headphone or using bone conduction so that sound is reproduced near the ears of a listener.
According to the technology described in the aforementioned patent document, low bass is reproduced near the ears of the listener using a headphone or bone conduction. Thus, the sound is heard by the listener at high volume, although the sound is not conveyed to the listener's neighbors.